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2018 O Level Chem P1 Q32 — Metals / Sacrificial Protection Solution

Metals / Sacrificial Protection 2018 O Level Pure Chemistry · Paper 1 · Q32

Question

Ships made from steel often have pieces of magnesium attached to them to protect the steel from corrosion. Which equation shows a reaction that occurs when magnesium is used to protect steel from corrosion?

AFe(s) → Fe²⁺(aq) + 2e⁻
BFe(s) → Fe²⁺(aq) + 3e⁻
CMg²⁺(aq) + 2e⁻ → Mg(s)
DMg(s) → Mg²⁺(aq) + 2e⁻

Correct answer: D

Video Solution

Explanation

Answer: D (\(\text{Mg(s)} \rightarrow \text{Mg}^{2+}\text{(aq)} + 2\text{e}^{-}\)). In sacrificial protection a more reactive metal is attached to the iron. Magnesium loses electrons more readily than iron, so it is preferentially oxidised and corrodes instead of the steel.

The protective process is the oxidation of magnesium: \(\text{Mg} \rightarrow \text{Mg}^{2+} + 2\text{e}^{-}\).

A and B show iron corroding, the very thing the magnesium prevents. C shows \(\text{Mg}^{2+}\) being reduced to magnesium, the reverse of what happens. Answer D.

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